1. Field of Invention
The present invention pertains to the field of systems. More particularly, this invention relates to motion control using time synchronization technology.
2. Art Background
Motion control systems are commonly employed in a wide variety of devices and systems including devices and systems used in industrial, office, and home environments. A motion control system may be defined as a control system that provides precise control of the movement of various actuating elements of a device or system. A controllable movement of an actuating element may be referred to as an axis or a degree of freedom. A typical motion control system includes an actuator for each axis and control circuitry that generates control values and provides the control values to the actuators as needed for a desired motion.
For example, a pen-based plotter usually includes an actuating element that moves a pen along an x axis and an actuating element that moves the pen along a y axis and these actuating elements provide two degrees of freedom for pen movement. Other degrees of freedom for pen movement in a plotter may be provided by actuating elements that change ink colors and actuating elements that move the pen into and out of contact with paper.
Prior motion control systems typically include a central controller which generates control values and provides the control values to the actuators in a sequence that will accomplish a desired motion. It is usually desirable that the control values be applied to the actuators with precise timing in order to precisely coordinate the motion among the axes. Any delay or skew in the application of control values to different actuators may cause deviation from the desire motion.
For example, a central controller in a plotter typically generates a series of x control values and a corresponding series of y control values when drawing a circle. It is usually desirable that each x control value be applied to the x actuator at the same time as the corresponding y control value is applied to the y actuator in order to prevent one axis or the other from deviating from the desired circle motion.
Prior motion control systems usually accomplish such precise coordination in the application of control values by employing control cards that enable the simultaneous application control values to multiple actuators. For example, a control card may have two output registers for applying control values to two different actuators. A central controller in such a system usually loads the output registers and then simultaneously triggers the outputs of both of the output registers to the actuators at the desired time. The tight coupling of the output registers on a card usually ensures that the corresponding control values are applied at substantially the same time.
Typically, such control cards are manufactured in standard numbers of axis, such as 2 or 4 axis, in order to be cost effective. If coordination is needed among more axes than a standard number then several cards may be necessary and some scheme must usually be devised for coordination among the cards. In addition, if portions of a motion control system are widely separated then coordination of the remote portions usually requires special attention to wiring or the use of specialized networks for communication among such prior control cards. Unfortunately, this usually increases the cost and complexity of a motion control system. On the other hand, fewer axes may be needed for a motion control system than are provided on such a prior control card. In that case the extra hardware purchased but not used usually adds unneeded costs to a motion control system. In addition, such prior control cards may make it difficult to upgrade a system if existing control cards cannot accommodate additional degrees of freedom.